The present invention relates generally to methods for heat treating and deformation processing of metals and alloys, and more particularly to a method for producing thin sheets of a single crystal superalloy by conditioning the cast alloy microstructure, pack rolling the alloy and post-rolling heat treatment.
Thin sheets of commercial nickel base superalloys have been used in critical components of advanced propulsion systems. These components demand high stiffness, tensile and creep strength and high cycle fatigue properties at temperatures up to 1800.degree. F. Commercial nickel base superalloys and oxide-dispersion strengthened alloys are quite satisfactory at low and intermediate temperatures, but are generally inadequate for prolonged use at high service temperatures. The invention solves or substantially reduces in critical importance shortcomings in the prior art by providing a method for producing single crystal superalloys in thin sheet form for use in fabricating components for high temperature applications. Directionally solidified single crystal superalloys of improved compositions exhibit high tensile and creep strength, crack growth resistance and fatigue resistance at the high operating temperatures of gas turbine engines. In accordance with the method described herein, thick cast sections of an alloy are repeatedly hot worked to thin sheet form without the occurrence of dynamic or static recrystallization in the alloy. The process is applicable generally to a wide range of nickel base superalloys for producing single crystal sheets and for controlling the extent of recrystallization in polycrystalline alloys. The principles of the invention may also be applied to the production of rods, wires or other special cross-section geometries
It is therefore a principal object of the invention to provide a heat treatment and hot deformation method for metals and alloys.
It is a further object of the invention to provide a method for heat treatment of nickel base superalloys.
It is yet another object of the invention to provide a method for producing thin single crystal sheets of nickel base superalloys.
It is a further object of the invention to produce thin sheets of nickel base superalloys having good high temperature tensile strength and creep and crack resistance.
It is yet another object of the invention to provide a method for controlling recrystallization in polycrystalline nickel base superalloys during hot working.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.